chrome----timing含義解釋

1. Queueing

   請求檔案順序的的排序

   什麼東西？

   浏覽器有線程限制的，發請求也不能所有的請求同時發送，是以，隊列喽。

   從添加到待處理隊列

   到實際開始處理的時間間隔标示

2. Stalled

   是浏覽器得到要發出這個請求的指令到請求可以發出的等待時間，一般是代理協商、以及等待可複用的TCP連接配接釋放的時間，不包括DNS查詢、建立TCP連接配接等時間等

3. DNS Lookup

   時間執行DNS查找。每個新域pagerequires DNS查找一個完整的往返。 DNS查詢的時間，當本地DNS緩存沒有的時候，這個時間可能是有一段長度的，但是比如你一旦在host中設定了DNS，或者第二次通路，由于浏覽器的DNS緩存還在，這個時間就為0了。

4. Initial connection

   建立TCP連接配接的時間，就相當于用戶端從發請求開始到TCP握手結束這一段，包括DNS查詢+Proxy時間+TCP握手時間。

5. Request sent

   請求第一個位元組發出前到最後一個位元組發出後的時間，也就是上傳時間

6. Waiting(TTFB)

   請求發出後，到收到響應的第一個位元組所花費的時間(Time To First Byte),發送請求完畢到接收請求開始的時間;這個時間段就代表伺服器處理和傳回資料網絡延時時間了。伺服器優化的目的就是要讓這個時間段盡可能短。

7. Content Download

   收到響應的第一個位元組，到接受完最後一個位元組的時間，就是下載下傳時間

官方解釋

（免于大家翻牆了）

先說請求的生命周期：

The primary phases of the request lifecycle are:

• Redirect

  Immediately begins startTime.

  If a redirect is happening, redirectStart begins as well.

  If a redirect is occurring at the end of this phase then redirectEnd will be taken.

• App Cache

  If it’s application cache fulfilling the request, a fetchStart time will be taken.

• DNS

  domainLookupStart time is taken at the beginning of the DNS request.

  domainLookupEnd time is taken at the end of the DNS request.

• TCP

  connectStart is taken when initially connecting to the server.

  If TLS or SSL are in use then secureConnectionStart will start when the handshake begins for securing the connection.

  connectEnd is taken when the connection to the server is complete.

• Request

  requestStart is taken once the request for a resource has been sent to the server.

• Response

  responseStart is the time when the server initially responds to the request.

  responseEnd is the time when the request ends and the data is retrieved.

然後在了解那張timing圖

• Queuing

  A request being queued indicates that:

  The request was postponed by the rendering engine because it’s considered lower priority than critical resources (such as scripts/styles). This often happens with images.

  The request was put on hold to wait for an unavailable TCP socket that’s about to free up.

  The request was put on hold because the browser only allows six TCP connections per origin on HTTP 1.

  Time spent making disk cache entries (typically very quick.)

  • Stalled/Blocking

    Time the request spent waiting before it could be sent. It can be waiting for any of the reasons described for Queueing. Additionally, this time is inclusive of any time spent in proxy negotiation.

    Proxy Negotiation

    Time spent negotiating with a proxy server connection.

  • DNS Lookup

    Time spent performing the DNS lookup. Every new domain on a page requires a full roundtrip to do the DNS lookup.

    Initial Connection / Connecting

    Time it took to establish a connection, including TCP handshakes/retries and negotiating a SSL.

  • SSL

    Time spent completing a SSL handshake.

    Request Sent / Sending

    Time spent issuing the network request. Typically a fraction of a millisecond.

  • Waiting (TTFB)

    Time spent waiting for the initial response, also known as the Time To First Byte. This time captures the latency of a round trip to the server in addition to the time spent waiting for the server to deliver the response.

    Content Download / Downloading

    Time spent receiving the response data.